Thunderbird is a total redesign of the Mozilla mail component to produce a cross-platform, stand-alone mail application using the XUL user interface language. It has many new features, among them the ability to customize your toolbars the way you want them. a new look and feel with a large number of downloadable themes which alter the appearance of the client, and the ability to add UI extensions.
The SeaMonkey project is a community effort to develop an all-in-one Internet application suite. It contains an Internet browser, email and newsgroup client with an included Web feed reader, HTML editor, IRC chat, and Web development tools, and is sure to appeal to advanced users, Web developers, and corporate users. It uses much of the Mozilla source code powering such successful siblings as Firefox, Thunderbird, Camino, Sunbird, and Miro.
The Courier mail transfer agent (MTA) is an integrated mail/groupware server based on open commodity protocols such as ESMTP, IMAP, POP3, LDAP, SSL, and HTTP. Courier provides ESMTP, IMAP, POP3, Webmail, and mailing list services within a single consistent framework. Individual components can be enabled or disabled at will. Courier implements basic Web-based calendaring and scheduling services integrated in the Webmail module.
Maildrop is a powerful email filter/delivery agent. It supports mbox-style mailboxes and maildirs (a mail storage format used by Qmail). Its mail filtering language supports RFC822 parsing and GDBM/Berkeley DB database files. The maildrop package also includes a command-line tool to perform various operations on MIME messages.
DocumentBurster is a tool for report distribution: split, merge, email, and FTP your reports. It has report delivery for Crystal Reports, SSRS Reporting Services, MS Access, Cognos, PeopleSoft, and SAP. It has report bursting for Pentaho, JasperReports, and BIRT. It can upload reports to MS SharePoint.
Anteater is a log analyser for MTA logfiles (such as those produced by sendmail and postfix). The tool is written in 100% C++ and is very easy to customize. Input, output, and the analysis are modular class objects with a clear interface. Currently, there are modules for reading the syslog format of sendmail and postfix that do up to eight useful analyses and write the result in plain ASCII or HTML, to stdout or to files.
Mail Avenger is a highly-configurable, MTA-independent SMTP server. It lets users run messages through filters like ClamAV and SpamAssassin during SMTP transactions, so the server can reject unwanted email before assuming responsibility for its delivery. Other unique features include TCP SYN fingerprint and network route recording, SPF (sender policy framework) as a general policy language, qmail-style delivery of extension addresses, validation of sender addresses through SMTP callbacks, mail-bomb protection, integration with kernel firewalls, and more.
GNU Mailutils is a rich and powerful protocol-independent mail framework. It contains a series of useful mail libraries, clients, and servers. These are the primary mail utilities for the GNU system. The central library is capable of handling electronic mail in various mailbox formats and protocols, both local and remote. Specifically, this project contains a POP3 server, an IMAP4 server, and a Sieve mail filter. It also provides a POSIX "mailx" client and a collection of other handy tools.